Magnetic field-induced ordering of a polymer-grafted biomembrane-mimetic hydrogel

A biomembrane-mimetic complex fluid that spontaneously orients in the prese nce of a magnetic field to yield a highly ordered lamellar structure is des cribed. Macroscopically oriented lamellae were produced by exploiting the i nverted thermoreversible phase transition of the material, that is, by alig ning the sample below the phase transition temperature (<16 degrees C) (i.e ., in the fluid, hexagonal micellar phase) and warming to produce the lamel lar gel phase in a 7.05 T magnetic field. The in situ field-induced alignme nt was studied by deuterium NMR. The lamellar domains were found to prefere ntially orient perpendicular to the applied field (negative order). Charact erization of the magnetic field-induced anisotropy by polarized optical mic roscopy and small-angle X-ray scattering/diffraction (SAXS) indicates that it persists even upon field termination. The directional alignment was flip ped by 90 degrees, with the lamellar domains oriented parallel to the field (positive order), simply by modifying the composition through the addition of a lanthanide ion (Eu3+). The system offers the opportunity to spacially organize both membrane and aqueous soluble proteins in an anisotropic matr ix, thereby facilitating structure and dynamic studies using a range of tec hniques, including magnetic resonance (both NMR as well as EPR), optical sp ectroscopy, and small-angle neutron and X-ray scattering.